U.S. patent number 6,052,586 [Application Number 08/920,596] was granted by the patent office on 2000-04-18 for fixed and mobile satellite radiotelephone systems and methods with capacity sharing.
This patent grant is currently assigned to Ericsson Inc.. Invention is credited to Peter D. Karabinis.
United States Patent |
6,052,586 |
Karabinis |
April 18, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Fixed and mobile satellite radiotelephone systems and methods with
capacity sharing
Abstract
A mobile satellite radiotelephone system uses some of the
capacity of a fixed satellite radiotelephone system in areas of
congestion. Capacity sharing is obtained by providing at least one
fixed retransmitting station in an area of overlap between the
fixed and mobile satellite radiotelephone systems. The fixed
retransmitting station retransmits communications between the fixed
satellite radiotelephone system and at least one of the mobile
radiotelephones in the vicinity thereof. The fixed retransmitting
station communicates with the mobile radiotelephones using the
mobile radiotelephone air interface, so that the communication is
transparent to the mobile radiotelephones.
Inventors: |
Karabinis; Peter D. (Cary,
NC) |
Assignee: |
Ericsson Inc. (Research
Triangle Park, NC)
|
Family
ID: |
25444029 |
Appl.
No.: |
08/920,596 |
Filed: |
August 29, 1997 |
Current U.S.
Class: |
455/427;
455/12.1; 455/13.1 |
Current CPC
Class: |
H04B
7/18563 (20130101) |
Current International
Class: |
H04B
7/185 (20060101); H04Q 007/20 () |
Field of
Search: |
;455/13.1,13.2,427,435,12.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bost; Dwayne D.
Assistant Examiner: Wyche; Myran K.
Attorney, Agent or Firm: Myers Bigel Sibley &
Sajovec
Claims
That which is claimed:
1. A satellite radiotelephone system comprising:
a fixed satellite radiotelephone system that communicates with a
plurality of fixed radiotelephones in a first communication
area;
a mobile satellite radiotelephone system that communicates with a
plurality of mobile radiotelephones in a second communication area,
wherein the first and second communication areas overlap to define
an overlapping area; and
at least one fixed retransmitting station in the overlapping area,
that retransmits communications from the fixed satellite
radiotelephone system directly to at least one of the mobile
radiotelephones and that retransmits communications directly
received from at least one of the mobile radiotelephones to the
fixed satellite radiotelephone system.
2. A satellite radiotelephone system according to claim 1:
wherein the fixed satellite radiotelephone system and the mobile
satellite radiotelephone system use a similar air interface;
and
wherein the at least one fixed retransmitting station is a fixed
repeater that relays communications between the fixed satellite
radiotelephone system and the at least one of the mobile
radiotelephones using the similar air interface.
3. A satellite radiotelephone system according to claim 1:
wherein the fixed satellite radiotelephone system uses a first air
interface and the mobile satellite radiotelephone system uses a
second air interface; and
wherein the at least one fixed retransmitting station converts
communications between the fixed satellite radiotelephone system
and the at least one of the mobile radiotelephones, between the
first air interface and the second air interface.
4. A satellite radiotelephone system according to claim 1 wherein
the fixed satellite radiotelephone system has higher capacity than
the mobile satellite radiotelephone system such that the at least
one fixed retransmitting station provides additional capacity for
the mobile satellite radiotelephone system using at least some of
the higher capacity of the fixed satellite radiotelephone
system.
5. A satellite radiotelephone system according to claim 4 wherein
the at least one fixed retransmitting station is located at a
congested area of the mobile satellite radiotelephone system in the
overlapping area, to thereby provide additional capacity for the
mobile satellite radiotelephone system in the congested area.
6. A satellite radiotelephone system comprising:
a first satellite radiotelephone system that communicates with a
plurality of first radiotelephones in a first communication
area;
a second satellite radiotelephone system that communicates with a
plurality of second radiotelephones in a second communication area;
and
at least one retransmitting station in the first area, that
retransmits communications from the first satellite radiotelephone
system directly to at least one of the second radiotelephones and
that retransmits communications directly received from at least one
of the second radiotelephones to the first satellite radiotelephone
system.
7. A satellite radiotelephone system according to claim 6:
wherein the first satellite radiotelephone system and the second
satellite radiotelephone system use a similar air interface;
and
wherein the at least one retransmitting station is a fixed repeater
that relays communications between the first satellite
radiotelephone system and the at least one of the second
radiotelephones using the similar air interface.
8. A satellite radiotelephone system according to claim 6:
wherein the first satellite radiotelephone system uses a first air
interface and the second satellite radiotelephone system uses a
second air interface; and
wherein the at least one retransmitting station converts
communications between the first satellite radiotelephone system
and the at least one of the second radiotelephones, between the
first air interface and the second air interface.
9. A satellite radiotelephone system according to claim 6 wherein
the first satellite radiotelephone system has higher capacity than
the second satellite radiotelephone system such that the at least
one retransmitting station provides additional capacity for the
second satellite radiotelephone system using at least some of the
higher capacity of the first satellite radiotelephone system.
10. A satellite radiotelephone system according to claim 9 wherein
the at least one fixed retransmitting station is located at a
congested area of the second satellite radiotelephone system, to
thereby provide additional capacity for the second satellite
radiotelephone system in the congested area.
11. A base station for a satellite radiotelephone system,
comprising:
means for locating the base station in an overlapping area of a
fixed satellite radiotelephone system that communicates with a
plurality of fixed radiotelephones and a mobile satellite
radiotelephone system that communicates with a plurality of mobile
radiotelephones; and
means for retransmitting communications from the fixed satellite
radiotelephone system directly to at least one of the mobile
radiotelephones and for retransmitting communications directly
received from at least one of the mobile radiotelephones to the
fixed satellite radiotelephone system.
12. A base station according to claim 11:
wherein the fixed satellite radiotelephone system and the mobile
satellite radiotelephone system use a similar air interface;
and
wherein the retransmitting means comprises repeating means for
relaying communications between the fixed satellite radiotelephone
system and the at least one of the mobile radiotelephones using the
similar air interface.
13. A base station according to claim 11:
wherein the fixed satellite radiotelephone system uses a first air
interface and the mobile satellite radiotelephone system uses a
second air interface; and
wherein the retransmitting means comprises means for converting
communications between the fixed satellite radiotelephone system
and the at least one of the mobile radiotelephones, between the
first air interface and the second air interface.
14. A base station according to claim 11 wherein the fixed
satellite radiotelephone system has higher capacity than the mobile
satellite radiotelephone system such that the base station provides
additional capacity for the mobile satellite radiotelephone system
using at least some of the higher capacity of the fixed satellite
radiotelephone system.
15. A base station according to claim 14 wherein the base station
is located at a congested area of the mobile satellite
radiotelephone system in the overlapping area, to thereby provide
additional capacity for the mobile satellite radiotelephone system
in the congested area.
16. A capacity sharing method for a fixed satellite radiotelephone
system that communicates with a plurality of fixed radiotelephones
in a first communication area; and a mobile satellite
radiotelephone system that communicates with a plurality of mobile
radiotelephones in a second communication area, wherein the first
and second communication areas overlap to define an overlapping
area, the capacity sharing method comprising the step of:
retransmitting communications from the fixed satellite
radiotelephone system directly to at least one of the mobile
radiotelephones and retransmitting communications directly received
from at least one of the mobile radiotelephones to the fixed
satellite radiotelephone system, in the overlapping area.
17. A method according to claim 16 wherein the fixed satellite
radiotelephone system and the mobile satellite radiotelephone
system use a similar air interface, the retransmitting step
comprising the step of:
relaying communications between the fixed satellite radiotelephone
system and the at least one of the mobile radiotelephones using the
similar air interface.
18. A method according to claim 16 wherein the fixed satellite
radiotelephone system uses a first air interface and the mobile
satellite radiotelephone system uses a second air interface, the
retransmitting step comprising the step of:
converting communications between the fixed satellite
radiotelephone system and the at least one of the mobile
radiotelephones, between the first air interface and the second air
interface.
19. A method according to claim 16 wherein the fixed satellite
radiotelephone system has higher capacity than the mobile satellite
radiotelephone system such that the retransmitting step provides
additional capacity for the mobile satellite radiotelephone system
using at least some of the higher capacity of the fixed satellite
radiotelephone system.
20. A capacity sharing method for a first satellite radiotelephone
system that communicates with a plurality of first radiotelephones
in a first communication area and a second satellite radiotelephone
system that communicates with a plurality of second radiotelephones
in a second communication area, the capacity sharing method
comprising the step of:
retransmitting communications from the first satellite
radiotelephone system directly to at least one of the second
radiotelephones and retransmitting communications directly received
from at least one of the second radiotelephones to the first
satellite radiotelephone system.
21. A method according to claim 20 wherein the first satellite
radiotelephone system and the second satellite radiotelephone
system use a similar air interface, the retransmitting step
comprising the step of:
relaying communications between the first satellite radiotelephone
system and the at least one of the second radiotelephones using the
similar air interface.
22. A method according to claim 20 wherein the first satellite
radiotelephone system uses a first air interface and the second
satellite radiotelephone system uses a second air interface, the
retransmitting step comprising the step of:
converting communications between the first satellite
radiotelephone system and the at least one of the second
radiotelephones, between the first air interface and the second air
interface.
23. A method according to claim 20 wherein the first satellite
radiotelephone system has higher capacity than the second satellite
radiotelephone system such that the retransmitting step provides
additional capacity for the second satellite radiotelephone system
using at least some of the higher capacity of the first satellite
radiotelephone system.
24. A capacity sharing method for a satellite radiotelephone
system, comprising the steps of:
locating a base station in an overlapping area of a fixed satellite
radiotelephone system that communicates with a plurality of fixed
radiotelephones and a mobile satellite radiotelephone system that
communicates with a plurality of mobile radiotelephones; and
retransmitting communication from the fixed satellite
radiotelephone system directly to at least one of the mobile
radiotelephones using the base station and retransmitting
communications directly received from at least one of the mobile
radiotelephones to the fixed satellite radiotelephone system.
25. A method according to claim 24 wherein the fixed satellite
radiotelephone system and the mobile satellite radiotelephone
system use a similar air interface, the retransmitting step
comprising the step of:
relaying communications between the fixed satellite radiotelephone
system and the at least one of the mobile radiotelephones using the
similar air interface.
26. A method according to claim 24 wherein the fixed satellite
radiotelephone system uses a first air interface and the mobile
satellite radiotelephone system uses a second air interface, the
retransmitting step comprising the step of:
converting communications between the fixed satellite
radiotelephone system and the at least one of the mobile
radiotelephones, between the first air interface and the second air
interface.
Description
FIELD OF THE INVENTION
This invention relates to radiotelephone systems and methods, and
more particularly to satellite radiotelephone systems and
methods.
BACKGROUND OF THE INVENTION
Satellite radiotelephone systems are being developed and deployed
at many locations around the world. Satellite radiotelephone
systems are often used where rugged terrain or lack of population
density may preclude use of conventional mobile radiotelephones or
fixed (wire) telephones. The design and operation of satellite
radiotelephone systems are well known to those having skill in the
art and need not be described further herein. It will be understood
that radiotelephone systems can be used for voice and data
communications, so that radiotelephones can include terminals such
as PCS terminals.
Satellite radiotelephone systems may be broadly classified into two
types: mobile satellite radiotelephone systems and fixed satellite
radiotelephone systems. In both types of systems, one or more
satellites are used to communicate with radiotelephones. The
satellites may be orbiting satellites or geostationary satellites.
A mobile satellite radiotelephone system is designed to communicate
with a plurality of mobile radiotelephones of similar size as
conventional cellular radiotelephones. In contrast, a fixed
satellite radiotelephone system is designed to communicate with a
plurality of fixed (nonmobile) radiotelephones using permanent or
semi-permanent fixed antennas which may be mounted on buildings or
homes.
The capacity of fixed satellite radiotelephone systems is generally
relatively large. The term "capacity" is used to refer to the
number of radiotelephones with which the satellite radiotelephone
system can communicate simultaneously.
The per satellite capacity of a satellite radiotelephone system is
generally limited by the amount of satellite power that is expended
per communications circuit in order to establish and maintain
communications with a radiotelephone. Another limiting factor of
satellite radiotelephone system capacity may be the available
frequency spectrum and the typically poor frequency reuse of
satellite radiotelephone systems.
Mobile satellite radiotelephone systems generally have a much lower
capacity than fixed satellite radiotelephone systems. In
particular, the regional and global mobile satellite systems that
are currently under development are generally quite limited in
capacity. Regional mobile satellite systems involving geostationary
satellites may have a capacity per satellite of about 10,000
simultaneous radiotelephone communications. Global mobile satellite
systems involving medium earth orbiting (MEO) or low earth orbiting
(LEO) satellites generally have even lower capacities per
satellite, typically three to four thousand simultaneous
radiotelephone communications.
A primary limitation in the per satellite capacity of mobile
satellite radiotelephone systems is the amount of power that is
expended per communication by the satellite payload in order to
establish and maintain communications with the small hand-held
mobile phones. Moreover, the practical limitations of forming a
very large number of spot beams from the satellite often limits
frequency reuse for mobile satellite radiotelephone systems. For
these and other reasons, the capacity of mobile satellite
radiotelephone systems is generally low.
Fixed satellite radiotelephone systems generally do not include
mobile telephone services. Rather, services are delivered to end
user homes or businesses via permanently or semi-permanently fixed
terminal installations. These installations generally include
directional antennas that in some cases are capable of tracking the
satellites.
Fixed satellite radiotelephone systems generally have higher
capacity than mobile systems. The fixed satellite radiotelephone
systems communicate using fixed user terminals which can use
relatively large end user antennas. Hence, the satellite power
required per equivalent communication can be lower for a fixed
system than for a mobile system. Furthermore, frequency allocations
for the fixed systems can be more liberal than those of mobile
systems for at least two reasons. First, fixed systems generally
operate at higher frequencies such as C-band or above, where the
frequency spectrum is not as crowded. Second, the user terminals
are fixed and use highly directional antennas so that angular
separation between satellites can be relied upon for frequency
reuse.
Due to the relatively limited capacity of mobile satellite
radiotelephone systems, capacity bottlenecks or "hot spots" may
develop in congested areas of the mobile satellite radiotelephone
system, where the mobile satellite radiotelephone system does not
have enough capacity to accommodate all users. It may be difficult
to increase the capacity of the mobile satellite system in these
congested areas.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide improved
fixed and mobile satellite radiotelephone systems and methods.
It is yet another object of the invention to provide mobile
satellite radiotelephone systems and methods which can increase
capacity in congested areas.
These and other objects are provided, according to the present
invention, by allowing a mobile satellite radiotelephone system to
use some of the capacity of a fixed satellite radiotelephone system
in areas of congestion. Capacity sharing may be obtained by
providing at least one fixed retransmitting station in an area of
overlap between the fixed and mobile systems. The station
retransmits communications between the fixed satellite
radiotelephone system and at least one of the mobile
radiotelephones in the vicinity thereof.
The present invention stems from the realization that in many parts
of the world, a fixed satellite radiotelephone system and a mobile
satellite radiotelephone system will include partially or filly
overlapping coverage areas. Accordingly, in these overlapping
areas, fixed retransmiting stations may be used to retransmit
communications between the fixed satellite radiotelephone system
and at least one of the mobile radiotelephones. The fixed
retransmiting station communicates with the mobile radiotelephones
using the mobile radiotelephone air interface so that the
communication is transparent to the mobile radiotelephones.
However, by providing at least one fixed retransmiting station,
capacity bottlenecks in the overlapping area can be reduced or
eliminated.
In particular, satellite radiotelephone systems according to the
invention, include a fixed satellite radiotelephone system that
communicates with a plurality of fixed radiotelephones in a first
communication area, and a mobile satellite radiotelephone system
that communicates with a plurality of mobile radiotelephones in a
second communication area. The first and second communication areas
overlap to define an overlapping area. At least one fixed
retransmiting station is provided in the overlapping area, that
retransmits communications between the fixed satellite
radiotelephone system and at least one of the mobile
radiotelephones. It will also be understood that even if the first
and second communication areas do not overlap, at least one fixed
retransmitting station may be provided in the first area, that
retransmits communications between the fixed satellite
radiotelephone system and at least one of the mobile
radiotelephones.
In one embodiment, the fixed satellite radiotelephone system and
the mobile satellite radiotelephone system use a similar air
interface. In this embodiment, the at least one fixed retransmiting
station can be a non-processing repeater and frequency translator
that relays communications between the fixed satellite
radiotelephone system and at least one of the mobile
radiotelephones.
In another embodiment, the fixed satellite radiotelephone system
uses a first air interface, and the mobile satellite radiotelephone
system uses a second air interface. In this embodiment, the at
least one fixed retransmitting station converts communications
between the fixed satellite radiotelephone system and the at least
one of the mobile radiotelephones, between the first air interface
and the second air interface. Accordingly, the fixed retransmitting
station may be a regenerative repeater which reformats the voice
and control channels. In either embodiment, at least one fixed
retransmitting station can provide additional capacity for the
mobile satellite radiotelephone system using at least some of the
capacity of the fixed satellite radiotelephone system in a
congested area of the mobile satellite radiotelephone system.
The fixed retransmitting station can provide a new type of base
station for a satellite radiotelephone system. The base station
includes means for locating the base station in an overlapping area
of a fixed satellite radiotelephone system and a mobile satellite
radiotelephone system. The base station also includes means for
retransmiting communications between the fixed satellite
radiotelephone system and at least one of the mobile
radiotelephones. The base station thereby can provide additional
capacity for mobile satellite radiotelephone system in a congested
area.
It will be understood by those having skill in the art that the
present invention may be used for capacity offload between any two
satellite radiotelephone systems. However, preferably, the present
invention is used to add capacity to a mobile satellite
radiotelephone system using resources of a fixed satellite
radiotelephone system. The systems may use a common satellite.
However, preferably, the present invention is used to add capacity
to a mobile satellite radiotelephone system including a first
satellite, using capacity resources of a fixed satellite
radiotelephone system including a second satellite. Associated
methods are also provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall diagram of satellite radiotelephone systems
and methods according to the present invention.
FIGS. 2A, 2B and 2C are schematic diagrams of frequency reuse in
satellite radiotelephone systems.
FIG. 3 is a block diagram of fixed retransmitting stations
according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention now will be described more fully hereinafter
with reference to the accompanying drawings, in which preferred
embodiments of the invention are shown. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
Referring now to FIG. 1, satellite radiotelephone systems and
methods according to the invention will now be described. As shown
in FIG. 1, a satellite radiotelephone system includes a fixed
satellite radiotelephone system 10 and a mobile satellite
radiotelephone system 30. The fixed satellite radiotelephone system
10 uses a first satellite 12 to communicate with a plurality of
fixed radiotelephones 14a, 14b and 14c in a first communication
area 16.
Fixed satellite radiotelephone communication system 10 communicates
with the plurality of fixed radiotelephones 14a-14c using a first
air interface 18, for example, C-band. Control of the fixed
satellite system 10 may be implemented by a feeder link 22 which
communicates with a gateway 24 and the public switched (wire)
telephone network (PSTN) 26.
It will be understood by those having skill in the art that the
fixed satellite radiotelephone system 10 may include more than one
satellite 12 and will typically include large numbers of fixed
radiotelephones 14. Moreover, the fixed radiotelephones are
generally implemented using a permanent or semi-permanent antenna
which may be coupled to multiple radiotelephones. Since the antenna
location is fixed, the capacity of the system may be large for the
reasons already described.
It will also be understood by those having skill in the art that
the feeder link 22 may include communications channels for voice
and data communications, and control channels. The control channels
are indicated by dashed lines in FIG. 1. The control channels may
be used to implement direct communications between fixed
radiotelephones, as shown for example between radiotelephones 14a
and 14b. The control channels may also be used to effect
communications between a fixed satellite radiotelephone 14c and a
mobile radiotelephone or a wire telephone via gateway 24 and PSTN
26. The feeder link 22 may use the same air interface or a
different air interface from the first air interface 18.
Still referring to FIG. 1, mobile satellite radiotelephone system
30 includes a second satellite 32 that communicates with a
plurality of mobile radiotelephones 34a-34d which are located in a
second communication area 36. Mobile satellite radiotelephone
system 30 communicates with mobile radiotelephones 34 using a
second air interface 38, for example at L-band or S-band.
Alternatively, the second air interface 38 may be the same as the
first air interface 18. However, the frequency bands associated
with the two air interfaces will generally be different.
A feeder link 42 may be used to communicate with other satellite,
cellular or wire telephone systems via Gateway 44 and PSTN 26. As
with fixed satellite system 10, the feeder link 42 may include
communications channels shown in solid lines and control channels
shown in dashed lines. The control channels may be used to
establish direct mobile-to-mobile communications, for example,
between mobile radiotelephones 34b and 34c. The control channels
may also be used to establish communications between mobile phones
34a and 34d and other satellite, mobile or wire telephone
systems.
As with the fixed satellite radiotelephone system 10, the mobile
satellite radiotelephone system 30 may employ more than one
satellite 32 and will generally communicate with large numbers of
mobile radiotelephones 34. The fixed and mobile satellite
radiotelephone system may also use a common satellite. The designs
of fixed and mobile satellite radiotelephone systems are well-known
to those having skill in the art and need not be described further
herein.
Still referring to FIG. 1, a congested area may be present in the
mobile satellite radiotelephone system 30 where a large number of
mobile radiotelephones 34e-34i are present. As also shown in FIG.
1, this congested area may be in an overlapping area 28 between
first communication area 16 and second communication area 36. If
this is the case, excess capacity from fixed satellite
radiotelephone system 10 may be offloaded to mobile satellite
radiotelephone system 30, according to the present invention.
Capacity offload may be provided by at least one fixed
retransmiting station 50a, 50b, that retransmits communications
between the fixed satellite radiotelephone system 10 and at least
one of the mobile radiotelephones. For example, as shown in FIG. 1,
first fixed retransmiting station 50a retransmits communications
between satellite 12 and mobile radiotelephones 34e and 34f. Second
fixed transmitting station 50b retransmits communications between
the satellite 12 and mobile radiotelephones 34g, 34h and 34i. It
will also be understood that the fixed retransmitting station need
not be located in an overlapping area as long as it can retransmit
communications between the fixed satellite radiotelephone system in
the first area, and the mobile radiotelephones.
The fixed retransmiting stations communicate with the satellite 12
using first air interface 18. However, they communicate with the
mobile radiotelephones using the second air interface 38.
Accordingly, from the standpoint of the mobile radiotelephones
38e-38i, communication is transparent. In other words, it is not
apparent to the mobile radiotelephones 34e-34i, or the users
thereof, that communications are occurring with the fixed satellite
radiotelephone system 10 rather than with the mobile satellite
radiotelephone system 30. However, additional capacity for the
mobile satellite radiotelephone system 30 in the congested areas
adjacent the fixed retransmitting stations 50 may be provided.
Operation of satellite radiotelephone systems and methods according
to the present invention will now be further described. According
to the invention, a mobile radiotelephone can establish a
communications link via the facilities of the fixed satellite
radiotelephone system, even though the mobile radiotelephone is
designed, manufactured and sold as a terminal intended for use with
the mobile satellite radiotelephone system. One or more operators
may offer both mobile and fixed telecommunications services over an
overlapping geographic area using two separate transponders in
separate satellites or within the same "hybrid" satellite, with one
transponder supporting mobile satellite radiotelephones and the
other supporting fixed satellite radiotelephones. As capacity "hot
spots" or congestion develops within certain spot beams of the
mobile radiotelephone system, the fixed system, with its much
higher capacity, can deploy fixed retransmiting stations to relieve
the capacity load of the mobile system.
Referring to FIG. 2A, an exemplary seven-cell frequency reuse
pattern, which may be used by the mobile satellite radiotelephone
system 30, is shown. Within each of the relatively large mobile
system cells, each typically being on the order of 400-600
kilometers in diameter, frequencies used by adjacent cells may be
locally retransmitted by the retransmitting station at reduced,
noninterfering power levels, and reused as shown in FIGS. 2B and
2C, thus substantially increasing the effective local capacity.
Accordingly, fixed retransmiting stations, located within the fixed
system's footprint or coverage area, receive signals from the fixed
satellite and retransmit these signals locally. Frequency
translation to bring the signals within the mobile system's
frequency band will generally be provided. In the reverse
direction, the fixed retransmiting stations receive signals from
mobile radiotelephones and retransmit signals from the mobile
radiotelephones to the fixed satellite system. Again, frequency
translation to bring the signals within the fixed system's
frequency band will generally be provided.
The mobile radiotelephones are ordinarily used with the mobile
satellite system. Accordingly, the fixed satellite system may need
to be configured to support the air interface used by the mobile
satellite radiotelephone system.
Alternatively, if different air interfaces are used by the fixed
and mobile satellite radiotelephone systems, the fixed
retransmitting station can perform a translation from one air
interface to the other, for example by demodulation and
remodulation. The fixed retransmiting station then becomes a
regenerative repeater which reformats communications channels as
well as control channels. However, if the mobile and fixed systems
both use substantially the same air interface, then the fixed
retransmitting station can function as a non-regenerative
repeater.
A preferred embodiment may use the simplest fixed retransmiting
station by having the fixed and mobile systems both utilize the
same air interface standard. Alternatively, the fixed system is
configured to support the mobile system air interface even though
the fixed system may be using another air interface for fixed
radiotelephone service.
Referring now to FIG. 3, a preferred embodiment of a fixed
retransmitting station 50 of FIG. 1 will be described. As shown in
FIG. 3, the fixed retransmitting station 50 uses a first antenna 52
to communicate with the satellite 12 using the first air interface
18 and a second antenna 54 to communicate with the mobile
radiotelephones 34 using the second air interface 38. Signals
received from antenna 52 are retransmitted to antenna 54 using
filter 62, low noise amplifier 64, frequency translator 66, low
noise amplifier 68, filter 72, power amplifier 74 and filter 76.
Signals received from antenna 54 are retransmitted to antenna 52
using filter 82, low noise amplifier 84, filter 98, frequency
translator 86, low noise amplifier 88, filter 92, power amplifier
94 and filter 96. The designs of these components are well-known to
those having skill in the art and need not be described further
herein. A local oscillator 100 is used in conjunction with a
frequency generator 102 for up and down conversion as
necessary.
Accordingly, a band of frequencies within the forward link band of
the fixed system which is set aside for retransmission by a
particular fixed retransmitting station, is amplified,
down-converted to the appropriate mobile system forward link band
in accordance with the frequency planning/reuse scheme as shown on
FIG. 2, amplified again and locally retransmitted. In the reverse
direction, signals received from the mobile radiotelephones are
amplified, up-converted to the appropriate fixed system return-link
band reserved for the fixed retransmiting station, amplified again
and transmitted to the satellite of the fixed satellite system
using the receive/transmit directional antenna 52 of the fixed
retransmitted station.
The fixed retransmitting station 50 forms a base station for a
satellite radiotelephone system, including means for locating the
base station in an overlapping area of a fixed satellite
radiotelephone system and a mobile satellite radiotelephone
communications system and means for retransmitting communications
between the fixed satellite radiotelephone system and at least one
of the mobile radiotelephones. If different air interfaces are
used, the retranslating means can comprise means for converting
communications between the first air interface and the second air
interface as well. Capacity sharing between fixed and mobile
satellite radiotelephone systems may thereby be provided.
In the drawings and specification, there have been disclosed
typical preferred embodiments of the invention and, although
specific terms are employed, they are used in a generic and
descriptive sense only and not for purposes of limitation, the
scope of the invention being set forth in the following claims.
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